In Patent Document 1, a device which includes an axial flow fan is described as a blower device used in cooling of a radiator of an automobile. In this axial flow fan, pressure fluctuation caused by a whole shape of a fan shroud is found to contribute to noise generation.
Thus, the blower device of Patent Document 1 includes a fan shroud provided with a cylindrical portion disposed a predetermined distance away from the fan on a radially outer side of the fan and a pressure-fluctuation restriction space having a fan shape centered at a center point of the fan. The pressure-fluctuation restriction space is formed by recessing the cylindrical portion to have the fan-shaped recess part. According to the shape of the fan shroud, the above-described pressure fluctuation can be moderated, and noise to be generated can be reduced.
The blower device described in Patent Document 1 includes the fan shroud having a rectangular shape and surrounding the fan having a circular shape. Hence, there are a long part and a short part in distance between an end part of the fan and an outer end part of the fan shroud, for example. Thus, an air amount drawn into the fan may be smaller in the short part than in the long part. Therefore, since the drawn air amount is uneven in a whole circumference of the end part of the fan, unequal air flows may be produced in the whole circumference of the fan, and so-called rotational noise that is noise associated with rotation of the fan may be generated.
Especially, in a vehicle driven by a motor, such as a hybrid vehicle or an electric vehicle, large noise such as engine sound is hardly generated or is not generated at all. Thus, the rotational noise of the fan mounted on the vehicle is easily transmitted to circumference of the vehicle recognizably, and may cause a noise problem of circumferential environment.